The invention is based on a method for topping off a reservoir chamber of a hydropneumatic pressure intensifier with oil, and on a known type of hydropneumatic pressure intensifier for performing the method.
In such hydropneumatic pressure intensifiers (German Patent 28 18 337 or German Offenlegungsschrift 28 10 894), hydraulic oil lost from leakage is replaced from time to time during operation by topping off the reservoir chamber. The hydraulic oil is pumped into the chamber from outside the pressure intensifier via a nipple; in the process, the spring-loaded reservoir piston is correspondingly displaced counter to the spring force. The spring force is usually generated by a mechanical helical spring or by a gas spring, in each case acting upon the end of the reservoir piston remote from the reservoir. Naturally, other means for generating the spring force are also possible.
One problem in topping off the reservoir chamber with oil is the venting of the reservoir chamber, which naturally is necessary when the chamber is first filled with hydraulic oil but may also be necessary when the hydraulic oil is topped off, specifically whenever air from the spring chamber has reached the reservoir chamber via the radial seals of the reservoir piston. Such harmful air may also have entered the reservoir chamber from the work chamber, for instance if the radial seals on the work piston are inadequately tight for the pneumatic pressures engaging the work piston.
Typically, venting of the reservoir chamber takes place through a vent bore, which is closed off by a vent screw that must be removed for hydraulic oil topping off and for intentional venting. Venting when topping off the oil is often unnecessary, however, so in that case the vent bore is not opened. Depending on the structural design of the reservoir spring and spring chamber, the reservoir piston may be displaced so far into the spring chamber, if the oil is not topped off carefully, that the radial outer seals overtake connection bores of the spring chamber, so that in the course of time they may become damaged. Unlike the vent bore, which has only a small diameter, these connection bores of the spring chamber are relatively large. These connection bores are used for instance for a gas spring, or if a helical spring is disposed in the spring chamber, they are used for the primary venting of the spring chamber.
If air is present in the reservoir chamber, however, then it can cause foaming of the hydraulic oil, leading to functional problems or inadequate pressure intensification.
Another disadvantage of these known pressure intensifiers is that if the topping off of the oil, which must of course always be done under a certain amount of pressure, is done without monitoring, the work piston is shifted out of its initial position, since after the end of the deflection stroke of the reservoir piston the hydraulic oil fed into the reservoir chamber escapes from the reservoir chamber into the work chamber. This necessitates draining the hydraulic oil, which is time-consuming. In any case, in the known pressure intensifiers, it is difficult to monitor the oil topping off process.